This work will involve assessing the molecular interactions of various amino acid and lipid functional groups of membrane macromolecules as they affect or determine specific biochemical and structural properties of the energy transducing membranes of plant chloroplasts. The principle approach will be to use chemical modifying reagents to alter the chemical structure and charge of a particular functional group; and then assess, through a variety of biochemical and structural assays, how that functional group may be involved in various membrane functions or as a structural determinant. The chloroplast system is advantageous because: (1) there is rapid and precise control over the energy source (light); (2) there are numerous biochemical function parameters such as partial electron transfer reactions, ion transport (H ion, K ion and Mg ions), photophosphorylation, and fluorescence, which reflect various aspects of membrane function in energy transduction; (3) membrane substructures within a single 100 A membrane are readily revealed by the freeze etch technique and may be studied in relation to energy transduction. Any advances in understanding which may come from this work will very likely be applicable to other membrane systems, such as the mitochondria, muscle and nerve, and the visual system. Certain basic principles of membrane organization and the interaction of membrane structure(s) to determine unique membrane functions probably will be common to many different membrane systems.